Distributed location sensor

ABSTRACT

A catheter configured for use with a magnetic field-based localization system includes a distributed location sensor that includes a plurality of individual location sensing coils electrically connected in series. The distributed location sensor has an effective magnetic center based on the individual characteristics of each location sensing coil. The effective magnetic center can be located in a space occupied by another structure such as an irrigation fluid delivery tube. The plurality of individual location sensing coils are generally smaller, thereby easing placement, and collectively, when connected in series, output a relatively strong and noise-free signal.

BACKGROUND

a. Technical Field

The instant disclosure relates generally to location sensors and moreparticularly to a distributed location sensor for use in a medicaldevice.

b. Background Art

Medical devices such as guidewires, catheters, introducers and the likewith magnetic field-based position sensors for device navigation areused in various medical procedures in the body. Typically, a magneticfield position sensor includes a generally cylindrical coil thattransforms an applied magnetic field into an induced voltage. Thisinduced voltage is used by an upstream localization system to computethe sensor's spatial position and orientation. For example only, it isknown to equip a catheter with one or more coils sufficient to allowdetection of five (5) or six (6) degrees-of-freedom (DOF), namely, athree-dimensional (3D) position (X, Y, Z) and two or three orientationparameters (e.g., roll, pitch, yaw).

In practice, repeatable and accurate location computation by thelocalization system is dependent on the availability of a clear inducedvoltage (i.e., a signal having a good signal to noise ratio). Moreover,there is a linear correlation between the sensor size and the inducedvoltage (and/or current) yielded by the sensor. Thus, with the ongoingprocess of miniaturization of such coil sensors, limits are beingreached where the induced voltages are inadequate for use in repeatableand accurate location computations.

The foregoing discussion is intended only to illustrate the presentfield and should not be taken as a disavowal of claim scope.

SUMMARY

According to various embodiments, at least one advantage of a medicaldevice that includes a distributed location sensor is increased designflexibility as to the placement of the components of the sensor withoutcompromise of the quality of the induced signal that is indicative ofthe location of the sensor.

In an embodiment, a medical device configured for use with a magneticfield-based localization system includes a shaft, an electrode, anobstruction, and a distributed location sensor. The shaft has a proximalend portion and distal end portion. The electrode is located at thedistal end portion of the shaft. The obstruction is located on or in theshaft and is selected from the group comprising a fluid delivery lumen,a pull wire lumen, a pull wire, a pull ring, a twisted pair cable, anirrigation passageway, a temperature sensor and electrical wiring. Thedistributed location sensor includes a plurality of location sensingcoils electrically connected in series and disposed in the distal endportion of the shaft. The plurality of location sensing coils has aneffective magnetic center located in a space occupied by theobstruction. The distributed location sensor is configured to produce asignal responsive to an applied magnetic field produced by thelocalization system where the signal is indicative of a location of theeffective magnetic center.

In an embodiment, a medical device configured for use with a magneticfield-based localization system includes a shaft, a tip electrode, afluid delivery lumen and a distributed location sensor. The shaft has aproximal end portion and distal end portion. The tip electrode has anirrigation passageway with a fluid inlet and at least one outlet on anouter surface of the electrode. The fluid delivery lumen is coupled atone end to the fluid inlet and is configured to be coupled to anirrigation fluid delivery system. The distributed location sensorincludes a plurality of location sensing coils electrically connected inseries and disposed in the distal end portion. The plurality of locationsensing coils has an effective magnetic center located in a spaceoccupied by the fluid lumen delivery lumen. The distributed locationsensor is configured to produce a signal responsive to an appliedmagnetic field produced by the localization system where the signal isindicative of a location of the effective magnetic center.

The foregoing and other aspects, features, details, utilities, andadvantages of the present disclosure will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic and block diagram view of a system illustrating anenvironment in which a medical device having a distributed locationsensor may be used.

FIG. 2 is a diagrammatic view of an exemplary catheter lab environmentin which the medical device of FIG. 1 may be used.

FIG. 3 is a diagrammatic view of an embodiment of a distributed locationsensor.

FIG. 4 is an exploded, isometric view of a distal portion of anirrigated ablation catheter that includes an embodiment of a distributedlocation sensor.

FIG. 5 is an enlarged, cross-sectional view of a portion of the catheterof FIG. 4 taken substantially along lines 5-5 when the catheter isassembled, showing a two-coil distributed location sensor embodiment.

FIG. 6A is a cross-sectional view of a location sensing coil having amagnetically-permeable core.

FIG. 6B is a cross-sectional view of a location sensing coil wound on atube.

FIG. 6C is a cross-sectional view of a location sensing coil having anair core.

FIG. 7 is an isometric view, with portions broken away, of a distalportion of an irrigated ablation catheter with a bendable tip electrodethat includes a further distributed location sensor embodiment.

FIG. 8 is an isometric view of a shank portion of the tip electrode ofFIG. 7 that includes a distributed location sensor embodiment.

FIG. 9 is an isometric view, with portions omitted for clarity, of adistal portion of the catheter of FIG. 7 showing an obstruction thatrestricts placement of a location sensor.

FIG. 10 is a schematic and block diagram view of an exemplary embodimentof a medical positioning system (MPS) that is shown in block form inFIG. 1.

DETAILED DESCRIPTION

Various embodiments are described herein to various apparatuses,systems, and/or methods. Numerous specific details are set forth toprovide a thorough understanding of the overall structure, function,manufacture, and use of the embodiments as described in thespecification and illustrated in the accompanying drawings. It will beunderstood by those skilled in the art, however, that the embodimentsmay be practiced without such specific details. In other instances,well-known operations, components, and elements have not been describedin detail so as not to obscure the embodiments described in thespecification. Those of ordinary skill in the art will understand thatthe embodiments described and illustrated herein are non-limitingexamples, and thus it can be appreciated that the specific structuraland functional details disclosed herein may be representative and do notnecessarily limit the scope of the embodiments, the scope of which isdefined solely by the appended claims.

Reference throughout the specification to “various embodiments,” “someembodiments,” “one embodiment,” or “an embodiment,” or the like, meansthat a particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment.Thus, appearances of the phrases “in various embodiments,” “in someembodiments,” “in one embodiment,” or “in an embodiment,” or the like,in places throughout the specification are not necessarily all referringto the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments. Thus, the particular features, structures, orcharacteristics illustrated or described in connection with oneembodiment may be combined, in whole or in part, with the features,structures, or characteristics of one or more other embodiments withoutlimitation given that such combination is not illogical ornon-functional.

It will be appreciated that the terms “proximal” and “distal” may beused throughout the specification with reference to a clinicianmanipulating one end of a medical device or instrument used to treat apatient. The term “proximal” refers to the portion of the device closestto the clinician (or to a robotic control configured to manipulate thedevice) and the term “distal” refers to the portion located furthestfrom the clinician. It will be further appreciated that for concisenessand clarity, spatial terms such as “vertical,” “horizontal,” “up,” and“down” may be used herein with respect to the illustrated embodiments.However, medical devices may be used in many orientations and positions,and these terms are not intended to be limiting or absolute.

Before proceeding to a detailed description of a distributed locationsensor, a general description will first be set forth of an exemplarysystem (FIGS. 1-2) in which a medical device with such a distributedlocation sensor may be used. Referring now to the drawings wherein likereference numerals are used to identify identical or similar componentsin the various views, FIG. 1 is a diagrammatic and block diagram view ofa system 10 that includes a medical device 26. Medical device 26 mayinclude any one of a wide range of invasive medical devices, such asthose devices configured for diagnostic, therapeutic and/or deliverypurposes.

Medical device 26, such as a catheter, may be configured to performvarious tracking, navigation, orientation and other location-relatedfunctions (e.g., using the catheter's location for superimposing arepresentation thereof on imaging of a region of interest). Thesefunctions are facilitated where the device is configured to allow alocalization system to determine its position and/or orientation. Asdescribed in the Background, such devices, in magnetic field-basedpositioning embodiments, are typically configured to include one or morelocation sensors, for example, a magnetic field-based location sensingcoil.

System 10 as depicted includes a main electronic control unit 12 (e.g.,one or more electronic processors) having various input/outputmechanisms 14, a display 16, an optional image database 18, alocalization system such as a medical positioning system (MPS) 20, anelectrocardiogram (ECG) monitor 22, a distributed location sensor 24 ₁,an optional patient reference sensor (PRS) 24 ₂, and an MPS-enabledelongate medical device 26. As shown, medical device 26 includes a mainbody 28 (e.g., a shaft) having a longitudinal axis, and which includes aproximal end portion 30 and a distal end portion 32.

Input/output mechanisms 14 may comprise conventional apparatus forinterfacing with a computer-based control unit, for example, a keyboard,a mouse, a tablet, a foot pedal, a switch or the like. Display 16 mayalso comprise conventional apparatus.

Medical device 26 may find use in navigation applications that useimaging of a region of interest. Therefore system 10 may optionallyinclude image database 18. Image database 18 may be configured to storeimage information relating to the patient's body, for example, a regionof interest surrounding a destination site for medical device 26 and/ormultiple regions of interest along a navigation path contemplated to betraversed by device 26 to reach the destination site. The image data indatabase 18 may comprise known image types including (1) one or moretwo-dimensional still images acquired at respective, individual times inthe past (pre-acquired imaging); (2) a plurality of relatedtwo-dimensional images obtained in real-time from an image acquisitiondevice (e.g., fluoroscopic images from an x-ray imaging apparatus, suchas that shown in exemplary fashion in FIG. 2) wherein the image databaseacts as a buffer (live fluoroscopy); and/or (3) a sequence of relatedtwo-dimensional images defining a cine-loop (CL) wherein each image inthe sequence has at least an ECG timing parameter associated therewithadequate to allow playback of the sequence in accordance with acquiredreal-time ECG signals obtained from ECG monitor 22. It should beunderstood that the foregoing are examples only and not limiting innature. For example, the image database 18 may also includethree-dimensional image data as well. It should be further understoodthat the images may be acquired through any imaging modality, now knownor hereafter developed, for example X-ray, ultra-sound, computerizedtomography, nuclear magnetic resonance or the like as well as a 3Dgeometry generated by the MPS itself.

MPS 20 is configured to serve as the localization system and thereforeis configured to determine positioning (localization) data with respectto one or more of MPS location sensors 24 _(i) (where i=1 to n) andoutput a respective location reading. The location readings may eachinclude at least one or both of a position and an orientation (P&O)relative to a reference coordinate system 34, which may be athree-dimensional reference coordinate system associated with MPS 20.For example, the P&O may be expressed as a position (i.e., a coordinatein three axes X, Y and Z) and an orientation (i.e., roll, yaw and pitch)of a magnetic field sensor (e.g., sensor 24) in a magnetic fieldrelative to a magnetic field generator(s) or transmitter(s). As will bedescribed in greater detail below, MPS 20 is also configured todetermine a P&O of an effective magnetic center 58 of distributedlocation sensor 24 ₁ (see FIG. 3).

MPS 20 determines respective P&O readings in the reference coordinatesystem 34 based on capturing and processing signals (e.g., signal 36)received from the magnetic field sensors 24 _(i) while such sensors aredisposed in a controlled, low-strength magnetic field 38. From anelectromagnetic perspective, these sensors develop a voltage that isinduced on the sensor residing in a changing magnetic field. Sensors 24_(i) are thus configured to detect one or more characteristics of themagnetic field(s) in which they are disposed and generate a respectiveindicative signal (e.g., one shown—signal 36), which can be furtherprocessed by MPS 20 to obtain a respective P&O thereof. As mentionedabove, sensor 24 ₁ is a distributed location sensor.

FIG. 1 shows another MPS sensor, namely, patient reference sensor (PRS)24 ₂, which, if provided in system 10, is configured to provide apositional reference of the patient's body so as to allow motioncompensation for gross patient body movements, imaging system movementsand/or respiration-induced movements. PRS 24 ₂ may be attached to thepatient's manubrium sternum, a stable place on the chest, or anotherlocation that is relatively positionally stable. Like MPS sensor 24 ₁,PRS 24 ₂ is configured to detect one or more characteristics of themagnetic field in which it is disposed, and wherein MPS 20 provides aP&O reading indicative of the PRS's position and orientation in thereference coordinate system 34. In an embodiment, PRS 24 ₂ can includethree magnetic field location sensing coils configured to detect thePRS's location in six degrees of freedom (6DOF).

The electro-cardiogram (ECG) monitor 22 is configured to continuouslydetect an electrical timing signal of the heart organ through the use ofa plurality of ECG electrodes (not shown), which may beexternally-affixed to the outside of a patient's body. The timing signalgenerally corresponds to the particular phase of the cardiac cycle,among other things. Generally, the ECG signal(s) may be used by the maincontrol unit 12 for ECG synchronized play-back of a previously capturedsequence of images (cine loop) stored in database 18. ECG monitor 22 andECG-electrodes may both comprise conventional components.

FIG. 2 is a diagrammatic view of system 10 as incorporated into anexemplary catheter laboratory. System 10 is shown as being incorporatedinto a fluoroscopic imaging system 40, which may include commerciallyavailable fluoroscopic imaging components. MPS 20 includes a magnetictransmitter assembly (MTA) 42 and a magnetic processing core 44 fordetermining location (P&O) readings. In an embodiment, the MTA 42 may beincorporated into the fluoroscopic imaging system by inclusion into theC-arm, for example as shown. In another embodiment, MTA 42 may be placedin other locations (e.g., not incorporated into the imaging system),such as, for example, under the patient table. MTA 42 is configured togenerate the magnetic field(s) in and around the patient's chest cavity,in a predefined three-dimensional space identified as a motion box 46.MPS sensors 24 _(i) as described above are configured to sense one ormore characteristics of the magnetic field(s) and when the sensors arein motion box 46, each generate a respective signal that is provided tomagnetic processing core 44. Processing core 44 is responsive to thesedetected signals and is configured to calculate respective P&O readingsfor each MPS sensor 24 _(i) in motion box 46. Thus, MPS 20 enablesreal-time tracking of each sensor 24 _(i) in three-dimensional space.One exemplary embodiment of MPS 20 will be described in greater detailbelow in connection with FIG. 10.

It should be understood that the computation of the sensor location istypically just an initial step, since it is frequently desired to thendetermine the device's spatial location (e.g., the location of thedevice's tip). To achieve this end goal, it is desirable to place thelocation sensor so as to lead to an accurate computation of the spatiallocation of the device. In many instances, it is thus desirable to placethe location sensor at a symmetric position within the device (e.g., ina catheter, at the distal end on the longitudinal axis). However, inmany instances, this desired position is already designated for anotherpurpose (e.g., irrigation fluid delivery) and may therefore already beoccupied by another structure (e.g., a fluid delivery lumen). Overall,the desired position for the location sensor is rarely available.

FIG. 3 is a diagrammatic view of an embodiment of distributed locationsensor 24 ₁. As described above, restrictions on the size and placementof a magnetic field location sensor present challenges in the overalldesign of a medical device. Embodiments consistent with the instantdisclosure involve embedding a plurality of sub-components of the sensorwithin the medical device in such a way that it bypasses the need tocompete for sought-after space with other structures in the medicaldevice. Instead of the conventional approach of first allocating adesired space for purposes of embedding a localization sensor, adifferent approach is taken where other structures are initially placed,and any remaining spaces (even if less desirable by conventionalstandards) are then allocated for deploying the sensing structure(s).Through this approach, components (or sub-components) that perform thesensing function are deployed “around” other functional structures inthe device.

As mentioned above, MPS 20 is configured to determine a P&O of a sensor.In this regard, a typical sensor is a solid state component thatincludes an electrical conductor (e.g., wire) having a predeterminednumber of turns wound on a tube or a magnetically permeable (e.g.,metal) rod or core. The sensor location represents an imaginarylocation, which is referred to herein as the effective center of thesensor. In a uniform sensor, the effective center will be aligned withthe sensor's center of mass. These factors make placement of aconventional single-component sensor on-axis near the distal end of anelongated medical device desirable, so that the detected sensor locationcan be easily and accurately used to compute the tip location.

Because of the competition for space in a medical device, it is alsodesirable that the sensor be relatively small so as to increase thechances that it can be placed at an optimal location in the device(i.e., so that the computed sensor location can thereafter be used toaccurately compute the location of the tip of the medical device).However, as the single-component sensor becomes smaller (e.g., a smallercoil), the induced signal is correspondingly reduced and can becomesubjected to noise.

In accordance with the present teachings, distributed location sensor 24₁ uses a plurality of inducing sub-components such as coils,electrically connected in series, to realize a composite (and aspatially distributed) location sensor. Splitting the sensing functioninto a plurality of inducing sub-components, when electrically connectedin series, allows for a reduction in size of each of the individualinducing components, thereby increasing the chances that eachsub-component will be able to be placed in the device in any remainingspace(s). In other words, since each of the individual inducingcomponents is reduced in size, there is greater flexibility in theirplacement within the device. Moreover, electrically connecting theplurality of inducing coils in series means that the individualcontributions from each inducing coil will be additive in the compositeoutput signal, and thus the distributed location sensor can be usedwithout compromising the overall signal strength.

Distributed location sensor 24 ₁ is configured to produce a signalresponsive to an applied magnetic field produced by a localizationsystem (e.g., MPS 20) indicative of the location of an effectivemagnetic center 58 of the sensor 24 ₁ in coordinate system 34. In anillustrative embodiment, sensor 24 ₁ includes a plurality of locationsensing coils designated 48 ₁, 48 ₂, . . . , 48 ₃ that are electricallyconnected in series. Each location sensing coil 48 _(i) is atwo-terminal device. A plurality of connecting wires 50 ₁, 50 ₂, 50 ₃,and 50 ₄ are provided to electrically connect location sensing coils 48_(i) in series. As a result, distributed location sensor 24 ₁, despitebeing composed of a plurality of individual location sensing coils 48_(i), still presents, with respect to an interface 52, as a two-terminaldevice, for example, having connecting lead ends 54, 56. The effectivemagnetic center 58 reflects the composite of the individual centers ofthe individual location sensing coils 48 _(i), which in turn is based onthe individual detection characteristics of each location sensing coil48 _(i). For example, the detection characteristics of a locationsensing coil may be influenced by the coil size (e.g., diameter,longitudinal length), the wire size, the number of turns, the presence(or absence) of a core (i.e., magnetically-permeable material), therelative orientation of one coil relative to another coil, and otherfactors known in the art. In one embodiment, the particular, as-designedposition of an effective magnetic center 58 within a medical device 26may be improved as to accuracy through a post-manufacture and pre-usecalibration procedure.

From a design perspective, the effective magnetic center 58 can beplaced in a desired position within medical device 26 but which isalready occupied by another structure. For example, such obstructions,for purposes of location sensor placement, may include, withoutlimitation, an on-axis irrigation fluid delivery lumen, an off-axisirrigation fluid delivery lumen, a pull wire lumen, a pull wire, a pullring, an electrical conductor, a twisted pair (TP) cable, a lumen for atwisted pair (TP) cable, an irrigation passageway, as well as otherstructures known in the art of medical devices (e.g., a temperaturesensor such as a thermocouple, electrical conductors, etc.).

FIG. 4 is an exploded, isometric view of a distal portion of anirrigated ablation catheter 26 a that includes an embodiment of adistributed location sensor, designated sensor 24 a. Catheter 26 a, thusequipped, is therefore configured for use with a magnetic field-basedlocalization system, such as MPS 20. In the illustrated embodiment,catheter 26 a includes a shaft 28 a (shown in phantom line in FIG. 4 andbest shown in FIG. 5) having a proximal end portion 30 a and a distalend portion 32 a.

In at least one embodiment, catheter 26 a further includes a diagnosticand/or therapeutic element, such as an ablation tip electrode 60 alocated at distal end portion 32 a of shaft 28 a, and as shown has alongitudinal axis 62 a associated therewith. Electrode 60 a isconfigured generally for delivery of ablative energy, such asradio-frequency (RF) electrical current, to a target tissue site (e.g.,the electrical current may flow from the electrode 60 a through thetarget tissue site to another electrode, for example, a body surfaceelectrode, patch electrode, another electrode on the catheter, or otherelectrodes as known). Electrode 60 a may comprise conventional materialsand configurations.

With continued reference to FIG. 4, electrode 60 a also includes anirrigation passageway 64 a (best shown in FIG. 5) with a fluid inlet 66a and at least one fluid outlet 68 a on an outer surface 70 a thereof.In the illustrated embodiment, electrode 60 a may be configured with aplurality of fluid outlets 68 a that are in fluid communication withirrigation passageway 64 a. Outlets 68 a (or “ports”) are configured toeject irrigation fluid near and around (or on) outer surface 70 a aswell as on or around the warming-up tissue.

Electrode 60 a further includes a proximal portion 72 a having areduced-diameter shank 74 a configured to receive shaft 28 a. Electrode60 a includes a first bore 76 a axially extending into shank 74 a and asecond bore 78 a extending into shank 74 a. Bores 76 a, 78 a areconfigured to hold location sensing coils as described below.

Catheter 26 a further includes an irrigation fluid delivery lumen 80 acoupled at one end to fluid inlet 66 a. Irrigation fluid delivery lumen80 a is configured to be coupled to an irrigation fluid delivery system82 (e.g., at the other end opposite the end that is coupled to inlet 66a). When activated, irrigation fluid delivery system 82 pumps irrigationfluid through lumen 80 a, which fluid is ultimately ejected from ports68 a. It should be understood, however, that the illustrated coolingstructure(s) are exemplary only and not limiting in nature—otherconfigurations and variations of irrigation passageways and/or fluidinlets/outlets are possible. As also shown, electrode 60 a iselectrically connected to an ablation generator 84, which is configuredto control generation and delivery of ablative energy destined forelectrode 60 a.

Ablation catheter 26 a illustrates the location sensor size andplacement challenges described above. For example, the desired space forplacement of a location sensing coil would be on-axis near electrode 60a; however, fluid delivery lumen 80 a already occupies this on-axisspace, and is therefore unavailable for use in placement of a locationsensing coil. As will be described below, an embodiment consistent withthe instant teachings provides for a distributed location sensor 24 athat includes a plurality of sub-components, for example, first andsecond location sensing coils 86 ₁, 86 ₂ that are disposed,respectively, in first and second bores 76 a, 78 a.

First and second location sensing coils 86 ₁, 86 ₂ cooperate to performthe overall location sensing function, resulting in the ability ofproducing a signal indicative of the location of an effective magneticcenter that resides in a space occupied by irrigation fluid deliverylumen 80 a and may be coincident with the lumen's longitudinal axis (seelongitudinal axis 62 a in FIG. 5, discussed below). In addition, bybreaking up the location sensor into sub-components, each sub-component(i.e., each one of the sensing coils 86 ₁, 86 ₂) can be reduced in sizerelative to a comparable single-coil sensor. This allows bores 76 a, 78a to be sized so as to completely receive each coil 86 ₁, 86 ₂. Thissizing approach prevents bulging of the shaft or other mechanicalinterference that could occur by attempting to fit a larger sensing coilinto the same space. In other words, for example, a comparablesingle-coil sensor would not completely fit within a single bore, evenif an off-axis placement were utilized, with the result that a portionof such a sensing coil would extend outside of the bore, causing spaceutilization complications.

FIG. 5 is an enlarged, cross-sectional view of a portion of catheter 26a taken substantially along lines 5-5 in FIG. 4 when the catheter isassembled. Each location sensing coil 86 ₁, 86 ₂ has a respective axis,designated 88 a, 90 a (the axes being directed into the paper). Neitherone of axes 88 a, 90 a are coincident with longitudinal axis 62 a onwhich lumen 80 a is disposed. However, it should be appreciated thatvariations are possible. In this regard, in an alternate embodiment, atleast one of the axes of the plurality of location sensing coils may becoincident with the longitudinal axis of the electrode/shaft. Forexample only, a distributed location sensor may include both an on-axis,hollow coil that surrounds a central irrigation fluid delivery lumenwhich would be co-axial therewith, in addition to the one or more ofoff-central-axis sensing coils described above. In addition, as shown,bores 76 a, 78 a may be radially offset from longitudinal axis 62 a bysubstantially equal distances. In an alternate embodiment, the radialoffset distances may be different. In addition, the respective detectioncharacteristics of sensing coils 86 ₁, 86 ₂ may be either (i) the same;or (ii) different.

FIG. 6A is a cross-sectional view of a location sensing coil that can beused in a distributed location sensor. In the illustrated embodiment,the location sensing coil includes a winding portion 92 a wound on asolid core 94 that comprises magnetically permeable material. In anembodiment, solid core 94 can alternatively comprise non-magneticallypermeable material.

FIG. 6B is a cross-sectional view of another location sensing coil thatcan be used in a distributed location sensor. In the illustratedembodiment, the location sensing coil includes a winding portion 92 awound on a tube or spool 96 that can comprise non-magnetically permeablematerial. In an embodiment, spool 96 can comprise magnetically permeablematerial.

FIG. 6C is a cross-sectional view of another location sensing coil thatcan be used in a distributed location sensor. In the illustratedembodiment, the location sensing coil includes a winding portion 92 chaving no spool or core (i.e., an air core).

FIG. 7 is an isometric view, with portions broken away, of an irrigatedablation catheter 26 b with a bendable tip electrode. Catheter 26 bincludes a distributed location sensor 24 b (best shown in FIG. 8 ascoils 108 ₂ and 108 ₃) and is thus configured for use with a magneticfield-based localization system (e.g., MPS 20). Catheter 26 b includes ashaft 28 b having a proximal end portion 30 b and a distal end portion32 b. Catheter 26 b further includes an ablation tip electrode 60 b atdistal end 32 b, which has a longitudinal axis 62 b associatedtherewith. Electrode 60 b is configured generally for delivery ofablative energy, such as radio-frequency (RF) electrical current, to atarget tissue site (e.g., the electrical current may flow from theelectrode 60 b through the target tissue site to another electrode, forexample, a body surface electrode or patch electrode, or otherelectrodes as known). Electrode 60 b may comprise conventional materialsand configurations, although as described above, may have a bendable tipas seen by reference to U.S. Pat. No. 8,187,267 (U.S. application Ser.No. 11/853,759, filed 11 Sep. 2007, herein the '759 application), andU.S. application Ser. No. 12/651,074, filed 31 Dec. 2009 (herein the'074 application). The '759 application and the '074 application areboth hereby incorporated by reference as though fully set forth herein.

FIG. 8 is an isometric view, with portions omitted for clarity, of aproximal end 72 b of electrode 60 b. Electrode 60 b further includes anirrigation passageway 64 b having a fluid inlet 66 b and one or morefluid outlets 68 b on an outer surface 70 (best shown in FIG. 7).Outlets 68 b (or “ports”) are configured to eject irrigation fluid nearand around (or on) outer surface 70 b. Electrode 60 b includes areduced-diameter shank 74 b at proximal end 72 b that is configured toreceive shaft 28 b on an outer surface thereof. As illustrated,electrode 60 b includes a first bore 76 b axially extending into shank74 b and a second bore 78 b extending into shank 74 b. Bores 76 b, 78 bare configured to hold location sensing coils as described in greaterdetail below.

With continued reference to FIG. 7, catheter 26 b further includes anirrigation fluid delivery lumen 80 b coupled at one end to fluid inlet66 b. Irrigation fluid delivery lumen 80 b is configured to be coupledto irrigation fluid delivery system 82, as shown in FIG. 4 in blockform. When activated, irrigation fluid delivery system 82 pumpsirrigation fluid through lumen 80 b, which fluid is ultimately ejectedfrom port or ports 68 b. Although not shown, electrode 60 a iselectrically connected to ablation generator 84, which is shown in FIG.4 in block form. It should be understood, however, that the illustratedcooling structure(s) are exemplary only and not limiting in nature—otherconfigurations and variations of irrigation passageways and/or fluidinlets/outlets are possible.

Electrode 60 b also includes a sidewall 98 that defines an interior 100(i.e., electrode 60 b is hollow). Sidewall 98 has one or more elongatedgaps 102 extending through sidewall 98. Gaps 102 are configured toprovide flexibility in sidewall 98 for bending movement of electrode 60b relative to longitudinal axis 62 b.

Ablation catheter 26 b, like ablation catheter 26 a, also illustratesthe size and placement challenges described above. For example, astructure in the form of lumen 80 b is already located in the desiredon-axis placement for a location sensing coil. Moreover, as shown inFIG. 9, catheter 26 b includes additional restrictions on the placementof a location sensor, in the form of a thermocouple 104 and itscorresponding connecting wires (not shown). A fluid lumen 106 is alsoshown. These items limit the available options with respect to theplacement of a location sensing coil.

Referring now to FIGS. 7-8, distributed location sensor 24 b of catheter26 b, in one embodiment, includes a hollow location sensing coil 108 ₁(FIG. 7) which is co-axial with longitudinal axis 62 b, and which has aneffective center at a desired location, namely, at a space occupied byfluid delivery lumen 80 b. However, sensing coil 108 ₁ may not beoptimal for subsequent detection of the tip location, since the tip isbendable and the effective center of the coil 108 ₁ may be too proximalto detect such bending. Accordingly, distributed location sensor 24 bmay further include, either as an addition to hollow sensing coil 108 ₁,or in lieu thereof, at least a plurality of additional location sensingcoils 108 ₂, 108 ₃.

In an embodiment, location sensing coil 108 ₁ is omitted altogether andthus the distributed location sensor 24 a includes the moredistally-located first and second location sensing coils 108 ₂, 108 ₃,which are disposed, respectively, in first and second bores 76 b, 78 bas shown in FIG. 8. First and second location sensing coils 108 ₂, 108 ₃together place an effective magnetic center in a space occupied byirrigation fluid delivery lumen 80 a. In addition, splitting thelocation sensor into sub-components allows each sub-component (i.e., 108₂, 108 ₃) to be reduced in size, thereby allowing bores 76 b, 78 b to besized so as to completely receive each coil 108 ₂, 108 ₃. This sizingapproach may prevent or reduce bulging of the shaft or other mechanicalinterference that could occur by attempting to fit a larger sensing coilinto the same space. In another embodiment, the location sensing coilsare disposed such that the effective magnetic center resides at alocation that allows detection of at least a part of the bendableportion of electrode 60 b. In sum, embodiments of a distributed locationsensor addresses the sizing and placement constraints described abovethat can exist in the design of a medical device.

FIG. 10 is a schematic and block diagram of one exemplary embodiment ofMPS 20, designated as a MPS 110, as seen by reference to U.S. Pat. No.7,386,339, hereby incorporated by reference as though fully set forthherein, having portions of which are reproduced below, which generallydescribes, at least in part, the MediGuide™ Technology systemcommercially offered by MediGuide Ltd. of Haifa, Israel and now owned bySt. Jude Medical, Inc. It should be understood that variations arepossible, for example, as also seen by reference to U.S. Pat. No.6,233,476, hereby incorporated by reference as though fully set forthherein. Another exemplary magnetic field-based MPS is the Carto™ systemcommercially available from Biosense Webster, and as generally shown anddescribed in, for example, U.S. Pat. No. 6,498,944, and U.S. Pat. No.6,788,967, both hereby incorporated by reference as though fully setforth herein. Accordingly, the following description is exemplary onlyand not limiting in nature.

MPS 110 includes a location and orientation processor 150, a transmitterinterface 152, a plurality of look-up table units 154 ₁, 154 ₂ and 154₃, a plurality of digital to analog converters (DAC) 156 ₁, 156 ₂ and156 ₃, an amplifier 158, a transmitter 160, a plurality of MPS sensors162 ₁, 162 ₂, 162 ₃ and 162 _(N), a plurality of analog to digitalconverters (ADC) 164 ₁, 164 ₂, 164 ₃ and 164 _(N) and a sensor interface166.

Transmitter interface 152 is connected to location and orientationprocessor 150 and to look-up table units 154 ₁, 154 ₂ and 154 ₃. DACunits 156 ₁, 156 ₂ and 156 ₃ are connected to a respective one oflook-up table units 154 ₁, 154 ₂ and 154 ₃ and to amplifier 158.Amplifier 158 is further connected to transmitter 160. Transmitter 160is also marked TX. MPS sensors 162 ₁, 162 ₂, 162 ₃ and 162 _(N) arefurther marked RX₁, RX₂, RX₃ and RX_(N), respectively. In an embodiment,any one or more of the sensors 162 ₁, 162 ₂, 162 ₃ and 162 _(N) can inturn comprise a respective distributed location sensor, as describedabove. Analog to digital converters (ADC) 164 ₁, 164 ₂, 164 ₃ and 164_(N) are respectively connected to sensors 162 ₁, 162 ₂, 162 ₃ and 162_(N) and to sensor interface 166. Sensor interface 166 is furtherconnected to location and orientation processor 150.

Each of look-up table units 154 ₁, 154 ₂ and 154 ₃ produces a cyclicsequence of numbers and provides it to the respective DAC unit 156 ₁,156 ₂ and 156 ₃, which in turn translates it to a respective analogsignal. Each of the analog signals is respective of a different spatialaxis. In the present example, look-up table 154 ₁ and DAC unit 156 ₁produce a signal for the X axis, look-up table 154 ₂ and DAC unit 156 ₂produce a signal for the Y axis and look-up table 154 ₃ and DAC unit 156₃ produce a signal for the Z axis.

DAC units 156 ₁, 156 ₂ and 156 ₃ provide their respective analog signalsto amplifier 158, which amplifies and provides the amplified signals totransmitter 160. Transmitter 160 provides a multiple axiselectromagnetic field, which can be detected by MPS sensors 162 ₁, 162₂, 162 ₃ and 162 _(N). Each of MPS sensors 162 ₁, 162 ₂, 162 ₃ and 162_(N) detects an electromagnetic field, produces a respective electricalanalog signal and provides it to the respective ADC unit 164 ₁, 164 ₂,164 ₃ and 164 _(N) connected thereto. Each of the ADC units 164 ₁, 164₂, 164 ₃ and 164 _(N) digitizes the analog signal fed thereto, convertsit to a sequence of numbers and provides it to sensor interface 166,which in turn provides it to location and orientation processor 150.Location and orientation processor 150 analyzes the received sequencesof numbers, thereby determining the location and orientation of each ofthe MPS sensors 162 ₁, 162 ₂, 162 ₃ and 162 _(N). Location andorientation processor 150 further determines distortion events andupdates look-up tables 154 ₁, 154 ₂ and 154 ₃, accordingly.

It should be understood that system 10, particularly the main electroniccontrol unit 12, as described above may include conventional processingapparatus known in the art, capable of executing pre-programmedinstructions stored in an associated memory, all performing inaccordance with the functionality described herein. Such an electroniccontrol unit may further be of the type having both ROM, RAM, acombination of non-volatile and volatile (modifiable) memory so that anysoftware may be stored and yet allow storage and processing ofdynamically produced data and/or signals.

Although only certain embodiments have been described above with acertain degree of particularity, those skilled in the art could makenumerous alterations to the disclosed embodiments without departing fromthe scope of this disclosure. Joinder references (e.g., attached,coupled, connected, and the like) are to be construed broadly and mayinclude intermediate members between a connection of elements andrelative movement between elements. As such, joinder references do notnecessarily infer that two elements are directly connected/coupled andin fixed relation to each other. Additionally, the terms “electricallyconnected” and “in communication” are meant to be construed broadly toencompass both wired and wireless connections and communications. It isintended that all matter contained in the above description or shown inthe accompanying drawings shall be interpreted as illustrative only andnot limiting. Changes in detail or structure may be made withoutdeparting from the invention as defined in the appended claims.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialsdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as explicitly set forth hereinsupersedes any conflicting material incorporated herein by reference.Any material, or portion thereof, that is said to be incorporated byreference herein, but which conflicts with existing definitions,statements, or other disclosure material set forth herein will only beincorporated to the extent that no conflict arises between thatincorporated material and the existing disclosure material.

What is claimed is:
 1. A medical device configured for use with amagnetic field-based localization system, comprising: a shaft having aproximal end portion and distal end portion; a tip electrode at thedistal end portion of said shaft, said electrode having an irrigationpassageway with a fluid inlet and at least one outlet on an outersurface of said electrode; a fluid delivery lumen coupled at one endthereof to the fluid inlet, said lumen being configured to be coupled toan irrigation fluid delivery system; and a distributed location sensorincluding a plurality of location sensing coils electrically connectedin series, each of said sensing coils being disposed in said distal endportion, said plurality of location sensing coils having an effectivemagnetic center located in a space occupied by said fluid lumen deliverylumen, said distributed location sensor being configured to produce asignal responsive to an applied magnetic field produced by thelocalization system indicative of a location of the effective magneticcenter.
 2. The medical device of claim 1 wherein said fluid inlet isdisposed on a longitudinal axis of said shaft, each of said plurality ofsensing coils having a respective coil axis, wherein at least one ofsaid coil axes is not coincident with said longitudinal axis.
 3. Themedical device of claim 2 wherein at least another one of said coil axesis coincident with said longitudinal axis.
 4. The medical device ofclaim 1 wherein at least first and second coils of said plurality ofsensing coils are asymmetric relative to a longitudinal axis.
 5. Themedical device of claim 1 wherein at least first and second coils ofsaid plurality of sensing coils are symmetric relative to a longitudinalaxis.
 6. The medical device of claim 1 wherein said electrode includes aproximal portion having a reduced-diameter shank configured to receivesaid shaft, said electrode including a first bore axially extending intosaid shank, said electrode including a second bore axially extendinginto said shank, wherein at least first and second coils of saidplurality of sensing coils are disposed in said first and second bore.7. The medical device of claim 6 wherein said first and second bores areradially offset from a longitudinal axis of said shaft by asubstantially equal distance.
 8. The medical device of claim 1 whereinat least one of said sensing coils includes a magnetically-permeablecore.
 9. The medical device of claim 1 wherein at least one of saidsensing coils comprises one of an air-core and a non-magneticallypermeable core.
 10. The medical device of claim 1 wherein the magneticfield-based localization system has a three-dimensional referencecoordinate system associated therewith, said location of said magneticeffective center includes a position in said reference coordinatesystem.
 11. The medical device of claim 1 wherein said signal is furtherindicative of an orientation of said medical device at said magneticeffective center.
 12. A medical device configured for use with amagnetic field-based localization system, comprising: a shaft having aproximal end portion and distal end portion; an electrode at the distalend portion of said shaft; an obstruction located on or in said shaftselected from the group comprising a fluid delivery lumen, a pull wirelumen, a pull wire, a pull ring, a twisted pair cable, an irrigationpassageway, a temperature sensor, and electrical wiring; and adistributed location sensor including a plurality of location sensingcoils electrically connected in series, each of said sensing coils beingdisposed in said distal end portion, said plurality of location sensingcoils having an effective magnetic center located in a space occupied bysaid obstruction, said distributed location sensor being configured toproduce a signal responsive to an applied magnetic field produced by thelocalization system indicative of a location of the effective magneticcenter.
 13. The medical device of claim 12 wherein a fluid inlet of saidelectrode is disposed on a longitudinal axis of said shaft, each of saidplurality of sensing coils having a respective coil axis, wherein atleast one of said coil axes in not coincident with said longitudinalaxis.
 14. The medical device of claim 12 wherein at least first andsecond coils of said plurality of sensing coils are asymmetric relativeto a longitudinal axis.
 15. The medical device of claim 12 wherein saidelectrode includes a proximal portion having a reduced-diameter shankconfigured to receive said shaft, said electrode including a first boreaxially extending into said shank, said electrode including a secondbore axially extending into said shank, wherein at least first andsecond one of said plurality of sensing coils are disposed in said firstand second bore.
 16. The medical device of claim 15 wherein said firstand second bores are radially offset from a longitudinal axis of saidshaft by a substantially equal distance.
 17. The medical device of claim15 wherein said first and second bores are radially offset from alongitudinal axis of said shaft by unequal distances.
 18. A medicaldevice configured for use with a localization system, comprising: anelongate member comprising a proximal portion and a distal portion; anda plurality of location sensors electrically connected in series andlocated in said distal portion, said plurality of location sensorshaving an effective center located in a space between said sensors, saidspace occupied by a structure connected to said distal portion, saidplurality of location sensors being configured to produce a signalresponsive to an applied field produced by the localization systemindicative of a location of the effective center.
 19. The medical deviceof claim 18 wherein said distal portion further comprises a therapeuticand/or diagnostic element.
 20. The medical device of claim 19 whereinsaid therapeutic and/or diagnostic element comprises an electrode andwherein said electrode comprises a sidewall having an interior whereinsaid sidewall has one or more elongated gaps extending through thesidewall, the one or more elongated gaps being configured to provideflexibility in the sidewall for bending movement of said electroderelative to a longitudinal axis of said elongate member, at least one ofsaid plurality of location sensors being disposed such that saidmagnetic effective center resides within a bendable portion of saidelectrode.